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The present invention relates to the measurement and monitoring of intracranial contents"" volume and intracranial pressure, and more particularly relates to an apparatus and method for non-invasive measurement of the brain parenchyma blood volume, brain tissue volume and intracranial pressure using ultrasonic pulses.
The measurement of intracranial pressure (ICP) is important in diagnosing and treating various pathophysiological conditions caused by head trauma, hemorrhage, tumours, inflammatory diseases and the like. Several techniques have been used to measure ICP. Conventional invasive ICP measurement techniques require surgical passage through the skull bone into the brain ventricles, parenchyma or the region between the skull and dura matter to implant a measuring transducer.
A non-invasive ICP measurement technique has been suggested that determines displacements of the tympanic membrane of the ear. However, it has been not possible to obtain a good correlation with ICP because determination of ICP by this method is complicated by the compressible air space between the pressure source and the interrogation point.
Another non-invasive ICP measurement method measures the electromagnetic impedance response of the brain to induced fields, and correlates the response to ICP. Such techniques are disclosed in U.S. Pat. Nos. 4,690,149 and 4,819,648 to Ko.
Another non-invasive ICP measurement technique that has been attempted involves ultrasonic imaging to detect relative displacements of tissue boundaries within the brain. The displacements may be associated with fluid build-up and compression or dilation of brain vessels, which permits determination of ICP through an independent calibration of compressibility. An alternate non-invasive ultrasonic technique involves the measurement of blood flow in the carotid artery by ultrasonic exitation of the artery and determination of Doppler frequency shift.
Various types of ultrasonic ICP measurement techiques are disclosed in U.S. Pat. No. 3,872,858 to Hudson et al., U.S. Pat. No. 4,043,321 to Soldner et al., U.S. Pat. No. 4,971,061 to Kageyama et al., U.S. Pat. No. 4,984,567 to Kageyama et al., U.S. Pat. No. 5,388,583 to Ragauskas et al., U.S. Pat. No. 5,411,028 to Bonnefous, U.S. Pat. No. 5,617,873 to Yost et al. and U.S. Pat. No. 5,919,144 to Bridger et al. Such techniques involve the transmission of ultrasonic waves typically having frequences on the order 0.1 . . . 0.5 or 5.0 MHz into the intracranial media.
Each of the patents cited above is incorporated herein by reference.
Despite the above-noted attempts to develop non-invasive ICP measurement technique a need still exists for a non-invasive ICP measurement apparatus and method which can measure ICP absolute value and all possible ICP waves with skull penetration, which poses no health risks during long term monitoring and which is accurate enough. On the other hand, ICP changes are caused by intracranial media components volume changes. These components are arterial and venous blood, cerebrospinal fluid (CSF), brain tissues and intersticial fluid. For the targeted therapy of raised ICP it is necessary to know the volume of which intracranial component is increased. It is still impossible to identify which intracranial component is the cause of ICP increment applying known ultrasonic ICP measuring methods and apparatus. The need exists for an intracranial blood volume, CSF volume and brain parenchyma tissue volume simultaneous measurement and monitoring. The only known method and apparatus for the measurement of blood volume inside the brain parenchymal acoustic path is our Parent Patent: U.S. Pat. No. 5,388,583.
However, known ultrasonic non-invasive ICP measuring apparatus and methods are affected by the head external tissues blood flow phenomena, the phenomena of frequency dependent ultrasound velocity and attenuation inside the external tissues, skull bones and intracranial media. The accuracy of known methods is limited also by the instrumental drifts of the ultrasonically measured values.
The objectives of this invention are:
apparatus and method for simultaneous, real-time, in situ measurement and monitoring of intraparenchymal blood volume, brain parenchyma tissue volume and ICP,
simultaneous, real-time and in situ measurement and monitoring of the ultrasonic pulses time-of-flight passing through the external tissues and skull bones,
elimination of such measured data from the measured data of ultrasound time-of-flight through the human head and getting at the first time the measured data about the dynamics of ultrasound time-of-flight from the one internal surface of dura matter to the other internal surface. In this case the non-invasively measured time-of-flight dynamic data depend on intracranial media acoustic properties only and do not depend on the acoustic properties of external tissues and skull bones,
simultaneous, real-time and in situ measurement and monitoring of the ultrasonic pulses internal period when these pulses are passing through the external tissues, skull bones and intracranial media,
determination of the frequency dependent attenuation of the ultrasound inside the external tissues, skull bones applying measured internal periods data and elimination of such characteristics from the attenuation data of the ultrasound transmission through the human head. Again, this let us get at the first time the attenuation dynamics in intracranial parenchymal acoustic path only without the influence of external tissues and skull,
simultaneous and real-time measurement of the time dependence of the instrumental delay of signal pulses in the circuits of transmitter, hybrid ultrasonic transducers, connecting cables and receiver,
elimination of the instrumental delay from the measured data,
identification and elimination of artefacts caused by ultrasonic transducers holder""sxe2x80x94mechanical frame movement caused by the patients head movements.